PSI - Issue 28

4

Author name / Structural Integrity Procedia 00 (2019) 000–000

Wim De Waele et al. / Procedia Structural Integrity 28 (2020) 253–265

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with  P the load range, B the thickness of the specimen, W the width of the specimen and F a shape factor depending on the relative crack size a/W defined in [9] .

Figure 2: Schematic illustration of ESET specimen extracted from a pipe made of offshore steel grade NV F460.

2.2. Instrumentation The main goal of this study is to quantify the fatigue crack growth (rate) during the long crack propagation phase of variable load amplitude tests. All fatigue tests have been performed on an MTS810 servo-hydraulic test machine with a load cell capacity of 100kN. The tests were performed in force controlled mode at a loading frequency of 10Hz. On-line determination of fatigue crack growth has been determined by the compliance technique using clip gauge measurements. An instrumented test specimen is shown in figure 3. This photograph also shows different electrical wires that were used for measurement of crack length using the direct current potential drop (DCPD) technique (De Tender, Micone, and De Waele 2016).The DCPD measurements are not further reported in this paper.

Figure 3: Photograph of an instrumented ESET specimen: (1) clip gauge, (2) marker lines, (3,4) input wires for direct electrical current, (5-6) DCPD probes, (7) reference probes to compensate for environmental effects, (8) back face electrical strain gauge.